The study of the long-term effects of radiation began as early as the 1920s. Studies have shown that ionizing radiation causes chromosomal mutations. A study of the health of residents of the Japanese cities of Hiroshima and Nagasaki showed that 12 years after the nuclear bombing, the frequency of oncological diseases in those people who were exposed to radiation increased. Moreover, the risk of developing cancer is not associated with the threshold model, when the disease occurs as a result of exceeding the "critical" value of the received dose. It increases linearly, even with short-term exposure. These phenomena are associated with the stochastic effect of radiation. According to scientists, any dose of radiation increases the risk of malignant tumors and genetic disorders.
What is the stochastic effect of ionizing radiation?
Radiation has a destructive effect on biological tissues. In modern science, there are 2 options for such consequences: deterministic and stochastic effects. The first type is also called predefined (from the Latin word determino - “define”), that is, the consequences arise when the dose threshold is reached. If it is exceeded, the risk of deviations increases.
Pathologies resulting from deterministic effects include acute radiation injury, radiation syndromes (bone marrow, gastrointestinal, cerebral), impaired reproductive function, and cataracts. They are noted as soon as possible after receiving a dose of radiation, less often - in the long term.
Stochastic, or random, effects (from the Greek word stochastikos - “guessing”) - these are consequences whose severity does not depend on the radiation dose. Dose dependence is manifested in an increase in the incidence of pathology among a population of living organisms. The probability of negative consequences exists even with short-term exposure.
Differences
Differences between the stochastic effect of radiation from the deterministic are described in the table below.
Criterion | Deterministic Effects | Stochastic effects |
Threshold dose | Manifested at high doses (> 1 Gy). If the threshold value is exceeded, the disease is inevitable (predetermined, determined). The severity of the lesion increases with increasing dose. | Observed at small and medium doses. Pathogenesis is dose-independent |
Damage mechanism | Cell death leading to impaired functioning of tissues and organs | Irradiated cells remain alive, but change and give mutant offspring. Clones can be suppressed by the body’s immune system. Otherwise, cancer develops, and with damage to germ cells - hereditary defects that shorten life expectancy |
Appearance time | Within hours or days after exposure | After the latent period. The disease is random. |
One of the features of stochastic phenomena is that they can occur simultaneously with chronic radiation sickness.
Kinds
Stochastic effects include 2 types of changes, depending on what kind of cells are affected:
- Somatic effects (malignant tumors, leukemia). They are detected during prolonged observation.
- Inherited effects recorded in descendants of exposed individuals. Occur due to damage to the genome in germ cells.
Both types of defects can appear both in the body of an irradiated person and in his offspring.
Cell mutation
Mutational processes in a cell exposed to radiation do not lead to its death, but stimulate genetic transformation. A so-called radiation-induced mutation arises - an artificially induced change in cell structures that are responsible for the transmission of hereditary information. They are permanent.
Cellular mutations are always present in natural, natural mechanisms. Thanks to them, children are different from their parents. This factor is very important for biological development. Spontaneous cancer and genetic pathologies are constantly present in the human population. Ionizing radiation is an additional agent that increases the likelihood of such changes.
In medical science, it is believed that even one transformed cell can initiate the development of a tumor process. DNA rupture and chromosomal aberrations can occur after a single ionization incident.
Diseases
A reliable connection between certain diseases and the accidental effects of radiation was proved only in the 90s of the XX century. Listed below are the stochastic effects of ionizing radiation:
- Malignant tumors of the skin, stomach, bone tissue, mammary glands in women, lungs, ovaries, thyroid gland, colon. Neoplastic diseases of the hematopoietic system.
- Non-tumor diseases: hyperplasia (excessive reproduction of cells) or aplasia (reverse process) of organs consisting of connective tissue (liver, spleen, pancreas and others), sclerotic pathologies, hormonal disorders.
- Genetic consequences.
Hereditary anomalies
In the group of genetic effects, 3 types of anomalies are distinguished:
- A change in the genome (the number and form of chromosomes), leading to the development of various abnormalities - Down syndrome, heart defects, epilepsy, cataracts and others.
- Dominant mutations that occur immediately, in the first or second generation of children.
- Recessive mutations. They arise only when the same gene mutates in both parents. Otherwise, genetic aberrations may not occur for several generations or may not occur at all.
Ionizing radiation leads to the occurrence of genetic instability in the cell due to disturbances in the system for repairing damaged DNA. A change in the normal course of biosynthesis entails a decrease in viability and the appearance of hereditary diseases. Cell genome instability is also an early sign of cancer.
Oncopathy level and latent period
Since stochastic effects are random in nature, it is impossible to reliably find out who they will develop from and who will not. The natural level of cancer in the human population is about 16% throughout life. This indicator is higher with an increase in the collective dose of radiation, but there is no exact data on this subject in medical science.
Since the development of malignant tumors is a multi-stage process, oncopathologies due to stochastic effects have a rather long latent (latent) period preceding the detection of the disease. So, with the development of leukemia, this figure is on average about 8 years. After a nuclear bombardment in the Japanese cities of Hiroshima and Nagasaki, thyroid cancer was diagnosed after 7-12 years, and leukemia after 3-5 years. Scientists believe that the duration of the latent period for malignant diseases in a certain location depends on the dose of radiation.
The consequences of genetic mutations
The consequences of hereditary mutations are divided into three groups according to the severity of the course:
- Major aberrations - death in the early embryonic and postpartum period, serious congenital malformations (craniocerebral hernias, lack of bones of the cranial vault, micro and hydrocephalus; underdevelopment or complete absence of the eyeball, abnormalities of the skeletal system - extra fingers, lack of limbs, etc.), developmental delay.
- Physical inferiority (instability in relation to the storage and transfer of genetic material from generation to generation, deterioration of the body's resistance to adverse external factors).
- Increased risk of developing malignant tumors as a result of a hereditary predisposition.